The research projects to be conducted concern the cellular processes by which progesterone and afferent tactile input derived from mating influence steroid hormone-sensitive neurons in the brains of female rats, resulting in changes in estrous behaviors. Regulation of estrous behavior in female rats is used as a model, because the ovarian steroid hormones, estradiol and progesterone have robust, predictable and well-studied interactions; estradiol increases behavioral response to progesterone, and progesterone facilitates the expression of estrous behaviors, and it then desensitizes the animal to further response. The effects of mating stimulation on progesterone-sensitive neurons will be studied, as this class of external environmental stimulation has robust effects on steroid hormone-dependent physiological and behavioral events. A variety of approaches from behavioral and neuroanatomical to cellular will be used to clarify the processes by which ovarian steroid hormones regulate the brain, primarily using this hormonally-regulated behavior as a model. A variety of techniques will be used including behavioral observation to determine the effects of particular hormonal, pharmacological and behavioral manipulations on this system, immunocytochemistry for identifying neurons containing steroid hormone receptors and/or that are responsive to particular hormonal, drug or behavioral treatments, in situ hybridization to examine mRNA levels for the steroid hormone receptors, and antisense oligonucleotides to inhibit selectively synthesis of progestin receptors and protein products of immediate early genes.